1. Field of the Invention
This invention relates to a process for preparing the alkali metal or ammonium salts of fatty hydroxamic acids.
2. Description of the Prior Art
The fatty hydroxamates to which the present invention is directed are effective reagents for carrying out a variety of hydrometallurgical operations, particularly exemplary of which is the flotation recovery of metals from oxidized minerals such as, for example, in the separation of copper from chrysocolla mineral ore.
Such hydroxamates can be readily derived by reacting hydroxylamine with a fatty acid ester to provide the corresponding hydroxamic acid which can then be neutralized with an appropriate base to obtain the hydroxamate. The foregoing procedure, however, is not adapted for the commercial production of hydroxamates since hydroxylamine in a hazardously unstable compound and thus not available for use in this form. Accordingly, hydroxylamine can only be used in any commercially adaptable process either as the sulfuric or hydrochloric acid salt thereof. The hydrochloric salt of hydroxylamine, because of its complete solubility in the polar organic solvents required for effecting the reaction concerned, is the hydroxylamine generating reagent conventionally used. Given a choice, however, one would prefer to use the sulfuric acid salt for economic reasons since the hydrochloride salt is made there from.
The drawback of employing the sulfuric acid salt of hydroxylamine in a process of the type to which this invention relates is because such salt is substantially completely insoluble in the polar organic solvents which, as mentioned above, must be used as the reaction medium in order to secure the reaction of the hydroxylamine with the fatty ester. It is nonethe less possible to carry out the underlying reaction in the presence of added water. However, this mode of operation results in a substantial formation of a soap, which not only adversely affects the yield of desired product, but also poses severe processing problems for the recovery thereof.
It is, accordingly, the object of this invention to prepare fatty acid hydroxamates using hydroxylamine sulfate as the source of hydroxylamine without undergoing the formation of soap, as is prone to occur in the prior art use of this material.